...throughout the movie, Thor was a hero. He never waivered, never hesitated, even after the Hulk almost killed him during their first encounter. It was Thor working overtime to stop the mindless Hulk. And what did Banner do that was so "heroic"? At first, he was too afraid (or unwilling) to merge again with the mindless Hulk....it was only when push came to shove, in order to save Thor, that Banner reluctantly did the right thing. Meh. Banner learned what it's like to be a true hero from Thor.
the whole idea behind it. Thor was tired of the cycle of battle and wanting an end to it. Banner proved himself the truer hero by willingly merging with the Hulk to show how true heroes act by giving up his own personal heaven to go back to his living nightmare. Hence, why Odin saluted him at the end. Add on that Odin was moments from waking up Banner saved Thor's life when he didn't have to. I was more or less their thinking.